However, other scientists have questioned the link between RNFL thickness and dementia, arguing that it does not reliably predict cognitive ability.

Researchers said an advantage of OCT tests is that they offer a relatively inexpensive and non-invasive way to screen for dementia.

But they said the tests should probably not be done in isolation to screen for dementia, as there would be people with thinner retinas who did not go on to experience cognitive decline.

Research ‘vital’

Dr Laura Phipps, from Alzheimer’s Research UK, said exploring how the eye can be used as a window into early brain changes was a growing area of research.

She said it would be interesting to see whether further studies showed that a greater likelihood of cognitive decline in those with thinner retinas also translated into an increased risk of dementia.

“With future treatments for Alzheimer’s and other dementias likely to be most effective when given early in the disease process, research into sensitive and non-invasive early markers of disease is vital.

“The brain is well protected by the skull and current approaches for detecting brain changes – such as brain scans – can be expensive to use routinely.

“While a diagnosis of dementia will always rely on results from a number of different tests, further studies should look at how sensitive OCT could be at identifying those most at risk of cognitive decline in the general population.”

The charity added that it was co-funding a study which analysed eye scans to look for features that could indicate the presence of dementia.